1. Technical Field
The present invention relates to a reader/writer forming a radio frequency identification (RFID) system.
2. Related Art
An RFID system including a contactless 1C card or a contactless tag such as an RF tag and a reader/writer has been known. Data and power are sent and received (two-way communication) between the tag and the reader/writer through electromagnetic induction.
In such RFID system, the reader/writer can communicate with one or more than one contactless tag located near the reader/writer. However, it cannot efficiently communicate with the contactless tag located away from the reader/writer at the same time with the tag located near the reader/writer.
JP-A-2000-36020 is an example of related art. In order to overcome such disadvantage, the example provides a plurality of antenna circuits for a transmission circuit of the reader/writer and switches between the transmission circuit and each of the plurality of the antenna circuits.
When the reader/writer has the plurality of the antenna circuits, there could be a case where antenna coils included in the antenna circuits should be placed adjacently each other or so as to overlap with the adjacent antenna coil. However, in this case, there could be a problem that the antenna coils interfere with each other.
Here, “the antenna coils interfere with each other” means the phenomenon that transmission power provided to the selected antenna coil in the reader/writer is absorbed by the other unselected antenna coil and the transmission power ends up decreasing, when the antenna coils are placed adjacently each other or so as to overlap with the adjacent antenna coil.
Consequently, the transmission power provided to the selected antenna coil in the reader/writer is not sufficiently transmitted to the antenna coil in the contactless tag.